In general, for the manufacture of semiconductor products such as an integrated circuit and the like, various processings including a film forming processing, an oxidation diffusion processing, an etching processing, a quality modification processing and an annealing processing are repeatedly carried out to a semiconductor wafer such as a silicon substrate or the like. A plasma processing apparatus is often used in performing processings of film forming, etching and ashing (see, e.g., JP2003-257933A). In recent years, there is a tendency to frequently use a microwave plasma processing apparatus, owing to an advantage that the apparatus is capable of stably generating high density plasma even in a high vacuum state of about 0.1 mTorr (13.3 mPa) to several tens of mTorr (several Pa). Such a plasma processing apparatus is disclosed in JP3-191073A, JP5-343334A, JP9-181052A, etc.
FIG. 11 is a cross sectional view schematically illustrating a structure of a conventional microwave plasma processing apparatus. In this microwave plasma processing apparatus 2, a mounting table 6 for supporting a semiconductor wafer W is provided within an evacuable processing vessel 4. A disc-shaped ceiling plate 8 made of microwave-transmitting aluminum nitride or quartz is air-tightly mounted to a ceiling portion of the processing vessel 4 that faces the mounting table 6. On a sidewall of the processing vessel 4, there is provided a gas nozzle 9 for introducing a processing gas into the vessel.
Installed above the ceiling plate 8 are a disc-shaped planar antenna member 10 having a thickness of about several millimeters and a wave retardation plate 12 made of a dielectric material and adapted to shorten the wavelength of a microwave in a radial direction of the planar antenna member 10. A multiple number of slot-shaped microwave radiation holes 14 are formed in the planar antenna member 10. A core conductor 18 of a coaxial waveguide 16 is connected to a center portion of the planar antenna member 10. A microwave of 2.45 GHz generated in a microwave generator 20 is converted to a specified vibration mode in a mode converter 22 and then guided to the planar antenna member 10. The microwave propagates radially through the antenna member 10 and is irradiated through the microwave radiation holes 14. Then, the microwave is introduced into the processing vessel 4 by penetrating the ceiling plate 8. Plasma originating from a processing gas is generated in a processing space A of the processing vessel 4 by the energy of the microwave. Using the plasma, a specified plasma processing such as etching or film forming is performed on a semiconductor wafer W.
In order to prevent an unnecessary film from adhering to an inner sidewall surface of the processing vessel when film forming is performed by plasma CVD (Chemical Vapor Deposition), or in order for an unnecessary film otherwise adhering thereto to be easily removed by dry cleaning, it is often necessary to keep the inner sidewall surface of the processing vessel at a considerably high temperature during the film-forming process. For example, if the temperature of the inner sidewall surface of the processing vessel remains low when a fluorocarbon film (interlayer dielectric film) of a low dielectric constant is formed on a wafer by plasma CVD using a CF-based gas, it is highly likely that an unnecessary film is deposited on the inner sidewall surface of the processing vessel. Furthermore, the unnecessary film adhering thereto at a low temperature is difficult to dislodge by dry cleaning.
With a view to solve this problem, a heater built-in type inner wall 24 having a thickness of 4 to 9 mm is provided along the inner sidewall surface at a position inwardly spaced apart several millimeters from the inner sidewall surface of the processing vessel 4. When forming a film, it is possible to prevent an unnecessary film from depositing on an inner surface of the inner wall by heating the inner wall 24 up to a temperature of about 100 to 200° C. In the meantime, a coolant passage 26 for allowing coolant to flow therethrough is provided in a sidewall of the processing vessel 4. By circulating the coolant through the coolant passage 26, the processing vessel 4 is kept at a safe temperature of about 90° C.
However, the solution noted above suffers from the following problems. First, since the space existing radially outwardly of the wafer W becomes narrow due to the presence of the inner wall 24, a gas stream flowing around the wafer W is changed and so is the radiant heat impinging on the wafer W. This may possibly reduce the in-plane uniformity of a film thickness. Furthermore, even though the inner wall 24 is heated up, it is unavoidable that an unnecessary film is deposited on the inner wall 24 in the course of processing a large number of wafers. If the distance between the wafer W and the inner wall 24 is small as noted above, there is also a possibility that the reproducibility of a film thickness becomes worse due to the change in a surface state of the inner wall, which would be caused by deposition of the unnecessary film. Although the above problems could be solved by increasing the size of the processing vessel 4 in proportion to the installation space of the inner wall 24, this is undesirable in that an increase in the size of the processing vessel 4 leads to an increase in the footprint of a processing apparatus.
Moreover, if a cooling operation of the sidewall of the processing vessel 4 is performed simultaneously with a heating operation of the inner wall 24 arranged adjacent to the processing vessel 4, the heating effect is set off against the cooling effect, thereby posing a problem in that energy efficiency becomes low by the unnecessary consumption of energy. An additional problem of the structure shown in FIG. 11 is its inability to perform temperature control to intentionally generate a temperature variation in a vertical direction of the processing vessel and, particularly, its inability to locally cool a specified portion.